feat(13-01): extend GraphDirectoryUser with UserType and add includeGuests parameter to directory service

- Add string? UserType as last positional parameter to GraphDirectoryUser record
- Add bool includeGuests = false parameter to IGraphUserDirectoryService.GetUsersAsync
- Branch Graph filter: members-only (default) vs all users when includeGuests=true
- Add userType to Graph Select array for MapUser population
- Update MapUser to include UserType from Graph User object
- Add MapUser_PopulatesUserType and MapUser_NullUserType tests

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

SharepointToolbox.Tests/Services/GraphUserDirectoryServiceTests.cs

@@ -31,7 +31,8 @@ public class GraphUserDirectoryServiceTests
             UserPrincipalName = "alice@contoso.com",
             Mail = "alice@contoso.com",
             Department = "Engineering",
-            JobTitle = "Senior Developer"
+            JobTitle = "Senior Developer",
+            UserType = "Member"
         };
 
         var result = GraphUserDirectoryService.MapUser(user);
@@ -41,6 +42,7 @@ public class GraphUserDirectoryServiceTests
         Assert.Equal("alice@contoso.com", result.Mail);
         Assert.Equal("Engineering", result.Department);
         Assert.Equal("Senior Developer", result.JobTitle);
+        Assert.Equal("Member", result.UserType);
     }
 
     [Fact]
@@ -52,7 +54,8 @@ public class GraphUserDirectoryServiceTests
             UserPrincipalName = "bob@contoso.com",
             Mail = null,
             Department = null,
-            JobTitle = null
+            JobTitle = null,
+            UserType = "Guest"
         };
 
         var result = GraphUserDirectoryService.MapUser(user);
@@ -62,6 +65,7 @@ public class GraphUserDirectoryServiceTests
         Assert.Null(result.Mail);
         Assert.Null(result.Department);
         Assert.Null(result.JobTitle);
+        Assert.Equal("Guest", result.UserType);
     }
 
     [Fact]
@@ -120,6 +124,44 @@ public class GraphUserDirectoryServiceTests
         Assert.Null(result.JobTitle);
     }
 
+    // ── MapUser: UserType mapping ──────────────────────────────────────────────
+
+    [Fact]
+    public void MapUser_PopulatesUserType()
+    {
+        var user = new User
+        {
+            DisplayName = "Eve Wilson",
+            UserPrincipalName = "eve@contoso.com",
+            Mail = "eve@contoso.com",
+            Department = "Sales",
+            JobTitle = "Account Executive",
+            UserType = "Member"
+        };
+
+        var result = GraphUserDirectoryService.MapUser(user);
+
+        Assert.Equal("Member", result.UserType);
+    }
+
+    [Fact]
+    public void MapUser_NullUserType_ReturnsNull()
+    {
+        var user = new User
+        {
+            DisplayName = "Frank Lee",
+            UserPrincipalName = "frank@contoso.com",
+            Mail = null,
+            Department = null,
+            JobTitle = null,
+            UserType = null
+        };
+
+        var result = GraphUserDirectoryService.MapUser(user);
+
+        Assert.Null(result.UserType);
+    }
+
     // ── GetUsersAsync: integration-level scenarios (skipped without live tenant) ──
 
     [Fact(Skip = "Requires integration test with real Graph client — PageIterator.CreatePageIterator " +